Lecture 16: Life in the Universe

Lecture 16:Lecture 16:Life in the UniverseLife in the Universe

Claire Max

November 23rd, 2010

Astro 18: Planets and Planetary Systems

UC Santa Cruz

Please remind me to take a break at 12:45 pm

Schedule for project presentations Schedule for project presentations (order within groups is up to you)(order within groups is up to you)

• Tuesday Nov 30thTuesday Nov 30th

• Thursday Dec 2Thursday Dec 2ndnd

Practicalities: When to use quotes, Practicalities: When to use quotes, citations, referencescitations, references

• To avoid plagiarism, you must give credit whenever To avoid plagiarism, you must give credit whenever you use:you use:

* another person’s idea, opinion, or theory;* another person’s idea, opinion, or theory;

* any facts, statistics, graphs, drawings—any pieces of * any facts, statistics, graphs, drawings—any pieces of information—that are not common knowledge;information—that are not common knowledge;

* quotations of another person’s actual spoken or written * quotations of another person’s actual spoken or written words; orwords; or

* paraphrase of another person’s spoken or written words.* paraphrase of another person’s spoken or written words.

• See handout, from See handout, from http://www.indiana.edu/~wts/pamphlets/plagiarism.shtml

http://www.indiana.edu/~wts/pamphlets/plagiarism.shtml

Practicalities: Final ExamPracticalities: Final Exam

• Tuesday December 7Tuesday December 7thth, noon to 3pm, noon to 3pm

• In this classroomIn this classroom

• Bring scientific calculatorsBring scientific calculators

Practicalities:Practicalities:Final Exam infoFinal Exam info

• Exam will consist of four parts:Exam will consist of four parts:

Part 1: Multiple Choice Questions Part 1: Multiple Choice Questions

Part 2: Questions based on images of solar system objects and Part 2: Questions based on images of solar system objects and phenomenaphenomena

Part 3: Construct a concept map of your own (more details on Part 3: Construct a concept map of your own (more details on next slide)next slide)

Part 4: Short-Answer QuestionsPart 4: Short-Answer Questions

Exam question on concept maps: Exam question on concept maps: please prepare ahead of time!please prepare ahead of time!

• In class we looked at concept maps that describe factors In class we looked at concept maps that describe factors influencing planetary surface geology. influencing planetary surface geology.

• Draw your own concept map describingDraw your own concept map describing factors influencing factors influencing planetary atmospheresplanetary atmospheres. . Indicate with arrows and text labels Indicate with arrows and text labels how these factors interact with each other to determine the how these factors interact with each other to determine the most important characteristics of the atmosphere.most important characteristics of the atmosphere.

• HintHint: Factors you might include:: Factors you might include:

– Planetary mass, surface gravity, rotation rate, distance from Planetary mass, surface gravity, rotation rate, distance from Sun, chemical composition, surface temperature, internal Sun, chemical composition, surface temperature, internal temperature, volcanism, greenhouse gases, cratering rate, temperature, volcanism, greenhouse gases, cratering rate, temperature compared with the boiling or freezing point of temperature compared with the boiling or freezing point of water, presence of life.water, presence of life.

Reminder: concept map for Reminder: concept map for planetary geologyplanetary geology

A loose end: How to remember A loose end: How to remember order of planets?order of planets?

• Mercury Venus Earth Mars (Asteroids) Jupiter Saturn Mercury Venus Earth Mars (Asteroids) Jupiter Saturn Uranus Neptune Uranus Neptune (not Pluto)(not Pluto)

• Mnemonic: a sentence with same first letters of words. Mnemonic: a sentence with same first letters of words. Helps remember a list. Helps remember a list.

• Example with Pluto: My very eager mother just sent us Example with Pluto: My very eager mother just sent us nine pizzas!nine pizzas!

• Extra credit: Come up with a new mnemonic without Extra credit: Come up with a new mnemonic without Pluto. Pluto.

– Can start at either inside (Mercury) or outside (Neptune) of Can start at either inside (Mercury) or outside (Neptune) of Solar System. (Starting at Neptune is worth a try….)Solar System. (Starting at Neptune is worth a try….)

– Nancy understood silly jokes after Mary explained very manyNancy understood silly jokes after Mary explained very many

• Bring your candidates to the Final ExamBring your candidates to the Final Exam

Practicalities: StargazingPracticalities: Stargazing

• Who hasn’t yet been to a stargazing party this Who hasn’t yet been to a stargazing party this quarter?quarter?

• I can try to arrange one if necessary.I can try to arrange one if necessary.

Outline of lectureOutline of lecture

• Life on EarthLife on Earth

– How did it begin?How did it begin?

– How did it change over time?How did it change over time?

• Life elsewhere in the Solar SystemLife elsewhere in the Solar System

– Mars? Venus? in past?Mars? Venus? in past?

– Jovian moons? now?Jovian moons? now?

• Life in other solar systemsLife in other solar systems

– Concept of a Habitable ZoneConcept of a Habitable Zone

• Search for Extra-Terrestrial Intelligence (SETI)Search for Extra-Terrestrial Intelligence (SETI)

Life on EarthLife on Earth

• When did life arise on Earth? When did life arise on Earth?

• How did life arise on Earth?How did life arise on Earth?

• What are the necessities of life?What are the necessities of life?

When did life arise on Earth?When did life arise on Earth?

Earliest Life FormsEarliest Life Forms

• Life probably arose on Earth more than Life probably arose on Earth more than 3.85 billion years ago, shortly after the end 3.85 billion years ago, shortly after the end of the late heavy bombardmentof the late heavy bombardment

• Evidence comes from carbon isotopesEvidence comes from carbon isotopes

• There is still contraversy about age of There is still contraversy about age of earliest life on Earthearliest life on Earth

– Hard to date the rock in which the carbon is Hard to date the rock in which the carbon is embeddedembedded

Use of Carbon isotope ratios to Use of Carbon isotope ratios to identify evidence of life in rocks identify evidence of life in rocks

• Isotopes: Atoms with the same number of protons in Isotopes: Atoms with the same number of protons in the nucleus (the same element), but different numbers the nucleus (the same element), but different numbers of neutrons.of neutrons.

• Normally, carbon-13 (C-13, with atomic weight 13), is Normally, carbon-13 (C-13, with atomic weight 13), is much rarer than C-12. much rarer than C-12.

• Biological processes concentrate C-12, so when Biological processes concentrate C-12, so when organic debris falls to the ocean floor, the C-12 to C-13 organic debris falls to the ocean floor, the C-12 to C-13 ratio rises still further in the sedimentary rock that ratio rises still further in the sedimentary rock that forms. forms.

• That ratio is preserved even in rocks so old that their That ratio is preserved even in rocks so old that their fossils have been ground up and destroyed.fossils have been ground up and destroyed.

Earliest Fossils in Sedimentary Rock Earliest Fossils in Sedimentary Rock are from ~3.5 billion years ago are from ~3.5 billion years ago

• Relative ages: deeper layers formed earlier.Relative ages: deeper layers formed earlier.

• Absolute ages: radiometric dating (isotope Absolute ages: radiometric dating (isotope ratios)ratios)

Fossils in Sedimentary Rock Fossils in Sedimentary Rock

• Rock layers of Grand Canyon record 2 Rock layers of Grand Canyon record 2 billion years of Earth’s historybillion years of Earth’s history

Earliest FossilsEarliest Fossils

• Oldest fossils show Oldest fossils show that bacteria-like that bacteria-like organisms were organisms were present over 3.5 present over 3.5 billion years agobillion years ago

• Photo: Photo: cyanobacteria cyanobacteria agglomorated agglomorated together in big together in big blobs called blobs called stromatolitesstromatolites

Origin of Life on EarthOrigin of Life on Earth

• Did it come from somewhere else?Did it come from somewhere else?

– PanspermiaPanspermia

• Or did it form here on EarthOr did it form here on Earth

– Chemical reactions to create building blocks of lifeChemical reactions to create building blocks of life

Could life have migrated to Earth?Could life have migrated to Earth?

• Venus, Earth, Mars have exchanged tons of Venus, Earth, Mars have exchanged tons of rock (blasted into orbit by impacts) rock (blasted into orbit by impacts)

• Some microbes can survive many years in Some microbes can survive many years in space...space...

• Theory that life came from beyond Earth is Theory that life came from beyond Earth is called “Panspermia” - “life everywhere”called “Panspermia” - “life everywhere”

Credit: Pawel Artymowicz

Geochemical (mineralogic) mapGeochemical (mineralogic) mapof Murchison (CM) Chondriteof Murchison (CM) Chondrite(carbonate shown in purple)(carbonate shown in purple)

Credit: Arizona State Univ.

Over 14,000 chemical compounds have been Over 14,000 chemical compounds have been identified in the Murchison Meteoriteidentified in the Murchison Meteorite

Comets: Dirty Snowballs Comets: Dirty Snowballs with lots of organic compoundswith lots of organic compounds

• Not yet clear whether Not yet clear whether there would have there would have been enough organic been enough organic compounds to “seed” compounds to “seed” life on Earthlife on Earth

Bacterial sporesBacterial spores

A highly resistant, resting phase displayed A highly resistant, resting phase displayed by some types of bacteria.by some types of bacteria.

Spores are formed in response to adverse Spores are formed in response to adverse changes in the environment. changes in the environment.

Original cell replicates its genetic material. One Original cell replicates its genetic material. One copy grows a tough coating. Outer cell copy grows a tough coating. Outer cell disintegrates, releasing spore which is now disintegrates, releasing spore which is now protected against a variety of traumas, protected against a variety of traumas, including extremes of heat and cold, and an including extremes of heat and cold, and an absence of nutrients, water, or air. absence of nutrients, water, or air.


Panspermia, continuedPanspermia, continued

The unmanned lunar probe The unmanned lunar probe Surveyor 3Surveyor 3 soft-landed on soft-landed on the Moon in 1967. In 1969, 2.5 yrs later, Apollo12 the Moon in 1967. In 1969, 2.5 yrs later, Apollo12 astronauts Pete Conrad and Alan Bean recovered the astronauts Pete Conrad and Alan Bean recovered the camera from camera from Surveyor 3Surveyor 3 and brought it back to Earth. and brought it back to Earth. The insulation covering its circuit boards contained 50 The insulation covering its circuit boards contained 50 to 100 viable specimens of to 100 viable specimens of Streptococcus mitisStreptococcus mitis, a , a harmless bacterium commonly found in the human nose, harmless bacterium commonly found in the human nose, mouth, and throat.mouth, and throat.

Conrad later commented: "I always Conrad later commented: "I always thought the thought the most significant thing that we most significant thing that we ever found on the ever found on the whole Moon was that whole Moon was that little bacteria who came little bacteria who came back and living back and living and nobody ever said anything and nobody ever said anything about it." about it."


Pawel Artymowicz

Alternative to PanspermiaAlternative to Panspermia

• The in situ formation of life here on Earth

• Predominant theory, presently

The Theory of EvolutionThe Theory of Evolution

• Fossil record shows that Fossil record shows that changes in species have changes in species have occurred through time. occurred through time.

• Darwin’s theory tells us Darwin’s theory tells us howhow evolution occurs: through evolution occurs: through natural selectionnatural selection..

• Theory strongly supported by Theory strongly supported by discovery of DNA: present in discovery of DNA: present in each cell nucleus, encodes our each cell nucleus, encodes our genetics.genetics.

• Evolution proceeds through Evolution proceeds through mutations of DNAmutations of DNA..

– Mutations induced by many Mutations induced by many factors: UV light, oxidants, ...factors: UV light, oxidants, ...

DNA encodes our genetics

Elements of Evolution: DefinitionsElements of Evolution: Definitions

• EvolutionEvolution:: the change over time of the the change over time of the genetic composition of populationsgenetic composition of populations

• Natural selectionNatural selection::populations of organisms populations of organisms

can change over the generations if can change over the generations if individuals having certain heritable individuals having certain heritable traits leave more offspring than traits leave more offspring than othersothers

• Evolutionary adaptationsEvolutionary adaptations::a prevalence of inherited a prevalence of inherited

characteristics that enhance characteristics that enhance organisms’ survival and organisms’ survival and reproductionreproduction

November 24, 1859

Evolution evidence: Evolution evidence: The Fossil RecordThe Fossil Record

• Succession of forms Succession of forms over time over time

• Transitional linksTransitional links

• Vertebrate descentVertebrate descent

Evolution evidence: Evolution evidence: Molecular BiologyMolecular Biology

• Similarities in DNA, Similarities in DNA, proteins, genes, and gene proteins, genes, and gene products between speciesproducts between species

• Common genetic codeCommon genetic code

• Reconstruct time Reconstruct time sequence of slow genetic sequence of slow genetic changes over timechanges over time

• ExtremelyExtremely compelling compelling evidence for evolutionevidence for evolution

Brief History of LifeBrief History of Life

• 4.4 billion years - early oceans form (no free oxygen in 4.4 billion years - early oceans form (no free oxygen in atmosphere)atmosphere)

• First life somewhere between 3.8 and 3.5 million yrs agoFirst life somewhere between 3.8 and 3.5 million yrs ago

• 3.5 billion years - cyanobacteria start releasing oxygen3.5 billion years - cyanobacteria start releasing oxygen

• 2.0 billion years - oxygen begins building up in atmosphere 2.0 billion years - oxygen begins building up in atmosphere (before that it was oxidizing surface rocks)(before that it was oxidizing surface rocks)

• 540-500 million years - Cambrian Explosion - many new 540-500 million years - Cambrian Explosion - many new speciesspecies

• 225-65 million years - dinosaurs and small mammals 225-65 million years - dinosaurs and small mammals (dinosaurs ruled)(dinosaurs ruled)

• Few million years - earliest hominidsFew million years - earliest hominids

Tree of LifeTree of Life

• Mapping genetic Mapping genetic relationships has led relationships has led biologists to discover this biologists to discover this new “tree of life.”new “tree of life.”

• Plants and animals are a Plants and animals are a small part of the tree. small part of the tree.

• Suggests likely Suggests likely characteristics of common characteristics of common “ancestor”“ancestor”..

• What was it?What was it?

• Genetic studies suggest that earliest life on Earth Genetic studies suggest that earliest life on Earth may have resembled the bacteria today found near may have resembled the bacteria today found near deep ocean volcanic vents (black smokers) and deep ocean volcanic vents (black smokers) and geothermal hot springs .geothermal hot springs .

Credit: David Webb, Univ. of Hawaii

Origin of Free Oxygen in Origin of Free Oxygen in AtmosphereAtmosphere

• Cyanobacteria Cyanobacteria paved the way for paved the way for more complicated more complicated life forms by life forms by releasing oxygen releasing oxygen into atmosphere via into atmosphere via photosynthesis photosynthesis

Credit: David Webb, Univ. of Hawaii

Thought QuestionThought Question

A.A. You’ll be eaten by dinosaurs.You’ll be eaten by dinosaurs.

B.B. You’ll suffocate because you’ll be You’ll suffocate because you’ll be unable to breathe the air.unable to breathe the air.

C.C. You’ll be consumed by toxic You’ll be consumed by toxic bacteria.bacteria.

D.D.Nothing. You’ll probably be just Nothing. You’ll probably be just fine. fine.

You have a time machine with a dial You have a time machine with a dial that you can spin to send you that you can spin to send you randomly to any time in Earth’s randomly to any time in Earth’s history. If you spin the dial, travel history. If you spin the dial, travel through time, and walk out, what is through time, and walk out, what is most likely to happen to you?most likely to happen to you?

Necessities for LifeNecessities for Life

• Nutrient sourceNutrient source

• Energy (sunlight, chemical reactions, internal Energy (sunlight, chemical reactions, internal heat)heat)

• Liquid water (or possibly some other liquid)Liquid water (or possibly some other liquid)

Hardest to find on other planets

David Grinspoon, Denver

Mars had liquid water in past; did it Mars had liquid water in past; did it (does it) have life?(does it) have life?

Norbert Schorghofer, U. Hawaii

Norbert Schorghofer, U. Hawaii

In our Solar System, Mars is best In our Solar System, Mars is best candidate for finding lifecandidate for finding life

• Exploration of Solar System has Exploration of Solar System has revealed…revealed…

• no sign of large life formsno sign of large life forms• we must search for we must search for microbialmicrobial life life

• Mars is best candidate:Mars is best candidate:

• Mars was apparently warm & wet in Mars was apparently warm & wet in its distant pastits distant past

• it had the chemical ingredients for it had the chemical ingredients for lifelife

• it has significant amounts of water it has significant amounts of water iceice

• pockets of underground liquid water pockets of underground liquid water mightmight exist if there is still volcanic exist if there is still volcanic heatheat

• Will we find life underground?Will we find life underground?

Mars at 2001 oppositionMars at 2001 oppositionHubble Space Telescope imageHubble Space Telescope image

Phoenix Lander on MarsPhoenix Lander on Mars

• Scratched surface, Scratched surface, uncovered iceuncovered ice

• Evaporated (sublimed) Evaporated (sublimed) when Sunlight had when Sunlight had shown on it for a whileshown on it for a while

In 2004, NASA Spirit and Opportunity Rovers sent home new mineral evidence of past liquid water on Mars.

The Martian Meteorite debateThe Martian Meteorite debate

Composition indicates Composition indicates origin on Mars. origin on Mars.

• 1984: meteorite ALH84001 found in Antarctica

• 13,000 years ago: fell to Earth in Antarctica

• 16 million years ago: blasted from surface of Mars

• 4.5 billion years ago: rock formed on Mars

Does the meteorite contain fossil Does the meteorite contain fossil evidence of life on Mars?evidence of life on Mars?

… most scientists not convinced

Could there be life on Europa Could there be life on Europa or other jovian moons?or other jovian moons?

Possible Life on Jovian MoonsPossible Life on Jovian Moons• Beneath its icy surface, Europa may have Beneath its icy surface, Europa may have

an ocean of liquid water.an ocean of liquid water.

• tidal heating keeps it warm tidal heating keeps it warm

• possibly with volcanic vents possibly with volcanic vents

• conditions may be similar to how Earth life conditions may be similar to how Earth life arosearose

• Ganymede & Callisto may also have Ganymede & Callisto may also have subsurface oceans, but tidal heating is subsurface oceans, but tidal heating is weaker.weaker.

• Titan has a thick atmosphere and oceans Titan has a thick atmosphere and oceans of methane & ethane.of methane & ethane.

• water is frozenwater is frozen

• perhaps life can exist in liquids other than perhaps life can exist in liquids other than water (??)water (??)

• Pockets of liquid water might exist deep Pockets of liquid water might exist deep underground.underground.

• Ganymede, Callisto also show some Ganymede, Callisto also show some evidence for subsurface oceans.evidence for subsurface oceans.

• Relatively little energy available for life, but still… Relatively little energy available for life, but still…

• Intriguing prospect of THREE potential homes for Intriguing prospect of THREE potential homes for life around Jupiter alone… life around Jupiter alone…

Ganymede Callisto

EnceladusEnceladus

•Ice fountains Ice fountains suggest that suggest that Enceladus may Enceladus may have a have a subsurface subsurface ocean.ocean.

Impacts and HabitabilityImpacts and Habitability

• Some scientists argue Some scientists argue that Jupiter-like that Jupiter-like planets are necessary planets are necessary to reduce rate of to reduce rate of impactsimpacts

• If so, then Earth-like If so, then Earth-like planets may be planets may be restricted to star restricted to star systems with Jupiter-systems with Jupiter-like planetslike planets

Climate and HabitabilityClimate and Habitability

• Some scientists argue Some scientists argue that plate tectonics that plate tectonics and/or a large Moon and/or a large Moon are necessary to keep are necessary to keep the climate of an the climate of an Earth-like planet stable Earth-like planet stable enough for lifeenough for life

The Bottom LineThe Bottom Line

We don’t yet know how important or negligible these concerns are.

Are We Alone?Are We Alone?

• Humans have speculated throughout history Humans have speculated throughout history about life on other worldsabout life on other worlds

• It was It was assumedassumed by many thinkers of the 17 by many thinkers of the 17thth & 18 & 18thth CenturiesCenturies

• Widely accepted by the public in the early 20Widely accepted by the public in the early 20thth CenturyCentury

• Scientists became more skeptical once we began to Scientists became more skeptical once we began to explore the planets in our own Solar Systemexplore the planets in our own Solar System

What is “life” ?What is “life” ?

• Surprisingly hard to define, if we want to avoid saying that all life Surprisingly hard to define, if we want to avoid saying that all life must be like must be like usus

• Reasonable defining characteristics: (not unique set)Reasonable defining characteristics: (not unique set)

– Ability to take energy from environment and change it from one form Ability to take energy from environment and change it from one form to anotherto another

– Highly organized. Chemicals found within bodies are synthesized Highly organized. Chemicals found within bodies are synthesized through metabolic processes into structures with defined purposes.through metabolic processes into structures with defined purposes.

– Regulate body and internal structures to certain normal parameters Regulate body and internal structures to certain normal parameters (e.g. temperature, acidity)(e.g. temperature, acidity)

– Respond to stimuliRespond to stimuli

– Self-replicating by making copies of themselvesSelf-replicating by making copies of themselves

– Grow and developGrow and develop

Where did “building blocks of life” come Where did “building blocks of life” come from?from?

• Building blocks of lifeBuilding blocks of life– Amino acids, nucleic acid bases, sugars, phosphoric acidAmino acids, nucleic acid bases, sugars, phosphoric acid

• Origins of the building blocks?Origins of the building blocks?

– Abiotic synthesis: Abiotic synthesis:

» Lab experiments in “reducing atmosphere” (little oxygen)Lab experiments in “reducing atmosphere” (little oxygen)

» Ingredients from volcanoes, sparked with electricity (as in Ingredients from volcanoes, sparked with electricity (as in lightning), rapidly formed amino acids and nucleic acidslightning), rapidly formed amino acids and nucleic acids

– Extraterrestrial origins:Extraterrestrial origins:

» Carbonaceous chondrites (meteorites) carry amino acidsCarbonaceous chondrites (meteorites) carry amino acids

» Lab experiments: mixture of ices (water, carbon dioxide, carbon Lab experiments: mixture of ices (water, carbon dioxide, carbon monoxide, methanol) was cooled to ten degrees above absolute monoxide, methanol) was cooled to ten degrees above absolute zero. Ice mixture was then exposed to strong ultraviolet radiation. zero. Ice mixture was then exposed to strong ultraviolet radiation. Formed amino acids and nucleic acids.Formed amino acids and nucleic acids.

Laboratory ExperimentsLaboratory Experiments

• Miller-Urey Miller-Urey experiment (and experiment (and more recent more recent experiments) show experiments) show that building blocks that building blocks of life can form of life can form spontaneously spontaneously under conditions of under conditions of early Earth. early Earth.

Which stars are most likely to have Which stars are most likely to have planets harboring life?planets harboring life?

• Must be old enough that life could arise Must be old enough that life could arise • More than a few x 10More than a few x 1088 years old, so not high-mass stars years old, so not high-mass stars

• They must allow for stable planetary orbitsThey must allow for stable planetary orbits– Probably rules out binary and multiple star systemsProbably rules out binary and multiple star systems

• They must have relatively large They must have relatively large habitable zoneshabitable zones– Surface temperature that allows water to exist as a liquidSurface temperature that allows water to exist as a liquid

Planets in habitable zonesPlanets in habitable zones

J.F. Kasting et al.

Extrasolar planets

Kepler space Kepler space mission will find mission will find many more!many more!

Impacts and HabitabilityImpacts and Habitability

• Some scientists argue Some scientists argue that Jupiter-like that Jupiter-like planets are necessary planets are necessary to reduce rate of to reduce rate of impacts.impacts.

• If so, then Earth-like If so, then Earth-like planets are restricted planets are restricted to star systems with to star systems with Jupiter-like planets.Jupiter-like planets.

Signs of lifeSigns of life

• Oxygen is highly reactiveOxygen is highly reactive

– Not stable in Earth’s atmosphere: maintained by Not stable in Earth’s atmosphere: maintained by plantsplants

– Earliest fossils were already photosynthesizingEarliest fossils were already photosynthesizing

» oxygen in atmosphere good indicator of life oxygen in atmosphere good indicator of life even in early stageseven in early stages

– Spectroscopic detection Spectroscopic detection possiblepossible

» in infra-red to reduce in infra-red to reduce background from starbackground from star

» good for 3-atom moleculesgood for 3-atom molecules

» detect COdetect CO22 (atmosphere), (atmosphere),

HH22O (oceans), OO (oceans), O33 (life) (life)

Simulated spectrum from DARWIN homepage

Spectral Signatures of LifeSpectral Signatures of Life

Earth

Venus

Mars

oxygen/ozoneoxygen/ozone

Renewed interest in “Astrobiology”Renewed interest in “Astrobiology”

• Reasons:Reasons:

• discovery of extrasolar planets indicate that discovery of extrasolar planets indicate that planetary systems are commonplanetary systems are common

• organic molecules are found throughout the Solar organic molecules are found throughout the Solar System and GalaxySystem and Galaxy

• geological evidence suggests life on Earth arose as geological evidence suggests life on Earth arose as soon as it was possiblesoon as it was possible

• discovery that living organisms can survive in the discovery that living organisms can survive in the most extreme conditions on Earthmost extreme conditions on Earth

Life beyond microbes: Life beyond microbes: Rare or Common?Rare or Common?

• Why animal life may be common:Why animal life may be common:• billions of stars in Galaxy have medium-size habitable zonesbillions of stars in Galaxy have medium-size habitable zones• planet formation theory: easy to form terrestrial planetsplanet formation theory: easy to form terrestrial planets• life on Earth began as soon as conditions allowed life on Earth began as soon as conditions allowed

• But some scientists propose “rare Earth hypothesis”But some scientists propose “rare Earth hypothesis”

• terrestrial planets may only form around stars with high abundances terrestrial planets may only form around stars with high abundances of heavy elementsof heavy elements

• the presence of our Jupiter deflects comets and asteroids from the presence of our Jupiter deflects comets and asteroids from impacting Earth, so animal life can evolve from microbesimpacting Earth, so animal life can evolve from microbes

• hence must have a Jupiter that did not migrate in towards the sunhence must have a Jupiter that did not migrate in towards the sun

• Earth has plate tectonics which allows the COEarth has plate tectonics which allows the CO22 cycle to stabilize cycle to stabilize climate, so animal life can evolveclimate, so animal life can evolve

• Moon, result of chance impact, keeps tilt of Earth’s axis stableMoon, result of chance impact, keeps tilt of Earth’s axis stable

• We will not know the answer until were have more data on other We will not know the answer until were have more data on other planets in the Galaxyplanets in the Galaxy

The Search for Extraterrestrial The Search for Extraterrestrial IntelligenceIntelligence

• What is the Drake equation and how is it What is the Drake equation and how is it useful?useful?

• What is SETI?What is SETI?

How many civilizations are out How many civilizations are out there?there?

Professor Frank Drake, UCSC (retired)

How many civilizations exist in our Galaxy How many civilizations exist in our Galaxy with whom we could make contact?with whom we could make contact?

• This simple formula is a variation on an equation first This simple formula is a variation on an equation first expressed in 1961 astronomer Frank Drake (UCSC)expressed in 1961 astronomer Frank Drake (UCSC)

• It is known as the It is known as the Drake equationDrake equation..

Number of civilizations = NHP

NHP = number of habitable planets in the Galaxy

x flife

flife = fraction of habitable planets which actually contain life

x fciv

fciv = fraction of life-bearing planets where a civilization has at some time arisen

x fnow

fnow = fraction of civilizations which exist now

How many civilizations exist in our Galaxy How many civilizations exist in our Galaxy with whom we could make contact?with whom we could make contact?

• Values of the terms in Drake Equation are unknownValues of the terms in Drake Equation are unknown

• The term we can best estimate is NThe term we can best estimate is NHPHP

• including single stars whose mass < few Mincluding single stars whose mass < few M AND… AND…• assuming 1 habitable planet per star, Nassuming 1 habitable planet per star, NHPHP ~ 100 billion ~ 100 billion• unless the “rare Earth” ideas are trueunless the “rare Earth” ideas are true

• Life arose rapidly on Earth, but it is our only exampleLife arose rapidly on Earth, but it is our only example

• fflifelife could be close to 1 or close to 0 could be close to 1 or close to 0

• Life flourished on Earth for 4 billion yrs before civilization Life flourished on Earth for 4 billion yrs before civilization arosearose

• value of value of ffcivciv depends on whether this was typical, fast, or slow depends on whether this was typical, fast, or slow

• We have been capable of interstellar communication for 50 We have been capable of interstellar communication for 50 years out of the 10 billion-year age of the Galaxyyears out of the 10 billion-year age of the Galaxy

• ffnownow depends on whether civilizations survive longer than this depends on whether civilizations survive longer than this

How does SETI work?How does SETI work?

SETI experiments look for deliberate signals from E.T.

SSearch for earch for EExtraxtraTTerrestrial errestrial IIntelligencentelligence

• IF we are typical of intelligent species and…IF we are typical of intelligent species and…

• IF there are many intelligent species out there…IF there are many intelligent species out there…

• then some of them might also be interested in making then some of them might also be interested in making contactcontact!!

• That is the idea behind the SETI program.That is the idea behind the SETI program.

• Radio telescopes listen for encoded Radio telescopes listen for encoded signals.signals.

• strategies to decide which stars to observestrategies to decide which stars to observe

• scan millions of frequencies at oncescan millions of frequencies at once

• We sent a powerful signal once in 1974 to We sent a powerful signal once in 1974 to the globular cluster M13the globular cluster M13

• now we just listennow we just listen

• SETI is privately fundedSETI is privately funded

– NASA dropped funding when a senator NASA dropped funding when a senator made fun of SETImade fun of SETI

Also “Optical SETI” - search for spectral Also “Optical SETI” - search for spectral lines typical of common laserslines typical of common lasers

• A search for intense A search for intense short laser pulses, short laser pulses, transmitted deliberately transmitted deliberately in our direction by in our direction by another civilization.another civilization.

• HarvardHarvard

• Lick ObservatoryLick Observatory

• PrincetonPrinceton

• Columbus OhioColumbus Ohio

We’ve even sent a few signals ourselves…We’ve even sent a few signals ourselves…

Earth to globular cluster M13: Hoping we’ll hear back in about 42,000 years!

You can participate in SETI@homeYou can participate in SETI@home

• Screensaver that analyzes results from Arecibo Screensaver that analyzes results from Arecibo radio telescope, sends back results to SETIradio telescope, sends back results to SETI

http://setiathome.ssl.berkeley.edu/

Interstellar Travel and Its Interstellar Travel and Its Implications for our CivilizationImplications for our Civilization

Goals for learning:Goals for learning:

• How difficult is interstellar travel?How difficult is interstellar travel?

• Where are the aliens?Where are the aliens?

Current Spacecraft are WAY too slowCurrent Spacecraft are WAY too slow

• Current spacecraft travel at <1/10,000Current spacecraft travel at <1/10,000cc; ; 100,000 years to the nearest stars100,000 years to the nearest stars

Pioneer plaque Voyager record

Difficulties of Interstellar TravelDifficulties of Interstellar Travel

• Far more efficient engines are needed.Far more efficient engines are needed.• Energy requirements are enormous.Energy requirements are enormous.• Ordinary interstellar particles become like Ordinary interstellar particles become like

cosmic rays.cosmic rays.• Social complications of time dilation.Social complications of time dilation.

(Fermi’s paradox)

Pawel Artymowicz

Where are the Aliens? Where are the Aliens? Fermi's paradoxFermi's paradox

• With current technology it is plausible that…With current technology it is plausible that…

• within a few centuries, we could colonize nearby starswithin a few centuries, we could colonize nearby stars

• in 10,000 years, we could spread out to 100s of light yearsin 10,000 years, we could spread out to 100s of light years

• in a few million years, human outposts throughout the Galaxyin a few million years, human outposts throughout the Galaxy

• Assume most civilizations take 5 billion yrs to arise:Assume most civilizations take 5 billion yrs to arise:

• the Galaxy is 10 billion yrs old, 5 billion yrs older than Earththe Galaxy is 10 billion yrs old, 5 billion yrs older than Earth

• IF there are other civilizations, the first could have arisen as IF there are other civilizations, the first could have arisen as early as 5 billion yrs agoearly as 5 billion yrs ago

• there should be many civilizations which are millions or there should be many civilizations which are millions or billions of years ahead of usbillions of years ahead of us

• they have had plenty of time to colonize the Galaxythey have had plenty of time to colonize the Galaxy

• So…where is everybody? Why haven’t they visited So…where is everybody? Why haven’t they visited us?us?

Possible Solutions to Possible Solutions to Fermi’s ParadoxFermi’s Paradox

• We are really aloneWe are really alone

• civilizations are extremely rare and we are the first one to arisecivilizations are extremely rare and we are the first one to arise

• then we are unique, the first part of the Universe to attain self-then we are unique, the first part of the Universe to attain self-awarenessawareness

• Civilizations are common, but have not colonizedCivilizations are common, but have not colonized

• interstellar travel is even harder or costlier than we imagineinterstellar travel is even harder or costlier than we imagine

• most civilizations have no desire to travel or colonizemost civilizations have no desire to travel or colonize

• most civilizations have destroyed themselves before they couldmost civilizations have destroyed themselves before they could

• There There isis a Galactic civilization a Galactic civilization

– it has deliberately concealed itself from usit has deliberately concealed itself from us

• We may know which solution is correct within your We may know which solution is correct within your generation!generation!

Main PointsMain Points

• Life elsewhere in the universe:Life elsewhere in the universe:

– None discovered yetNone discovered yet

– Building blocks seen throughout interstellar spaceBuilding blocks seen throughout interstellar space

– Microbial life seems VERY resilient here on EarthMicrobial life seems VERY resilient here on Earth

– Promising other sites for life in our Solar SystemPromising other sites for life in our Solar System

– Kepler spacecraft is searching for Earth-like planets: Kepler spacecraft is searching for Earth-like planets: big announcement in February!big announcement in February!

• Big unknowns: are conditions for animal-type Big unknowns: are conditions for animal-type life common, or rare?life common, or rare?

Lecture 16: Life in the Universe

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Transcript of Lecture 16: Life in the Universe